1. Field of the Invention
The present invention relates to an image processing method enabling an image corresponding to image data generated by various applications to be printed by a printer. More specifically, the invention relates to an image processing method for image data including a compressed image.
2. Description of the Related Art
With the digitalization of printing processing, Desktop Publishing (DTP) is rapidly expanding. With DTP, page layout are made by operations such as creating, processing, and editing of an image using various applications on processors such as personal computers or workstations. Film used for exposing a printing plate is generated on the basis of the page layout (image setter, RIP for plate), and a press plate for printing is generated by directly writing data to a printing plate, known as Computer to Plate (CTP).
In the operation, an image in a page layout is separated into colors of C, M, Y, and K and a printing plate is exposed on the basis of the respective image data, thereby generating a press plate obtained by forming a halftone image on the printing plate. A predetermined color ink is applied to the press plate of each color, and overlapping printing is performed, thereby forming a color image on printed matter.
Prior to printing using an actual press plate, a proof is made. A page layout is displayed on a monitor or a printout is obtained by a printer such as a laser printer or a page printer by using a functions such as the WYSIWYG. In a regular printer, printing is performed based on a composite output. In order to reproduce the printout obtained by using the press plate, however, the composite output cannot be used. Instead, it is necessary to use a separation output obtained by separating an image into the colors C, M, Y, and K identical to those created at the time of press plate generation.
Image data has to be color-separated into colors C, M, Y, and K with an application for DTP or an image processing apparatus, called Raster Image Processor (RIP), having functions for converting image data or drawing command into bit map data.
When creating a layout (page layout) with a DTP application, high-resolution image data is used to obtain sufficient picture quality on a printed matter. However, since the data amount (image size) of high-resolution image data is so large, processing or transmitting the image data when printing drawn data or image data on the page layout takes a long time.
As methods for solving such problems, various image-replacing servers for using low-resolution image at the time of layout have been proposed (for example, see Japanese Patent Application Laid-open (JP-A) Nos. 2000-341503 and 2000-341504).
In these proposals, however, a high-resolution image has to be pre-registered for replacement. In the cases such that an image is corrected frequently, the images period of usage is short, or an image is used only once, a registered image has to be managed frequently, which is problematic because management becomes a time-consuming hassle.
In recent years, advances in image compressing have increased the popularity of the technology. Image data subjected to high compression in formats such as JPEG posses many merits, so compressed image data is often used for creating page layout.
Technology using JPEG compression includes JPEG encoding of an Encapsulated PostScript (EPS) file (hereinafter, referred to as EPS (JPEG)). Images in an EPS conventionally used for DTP are compressed in the JPEG format.
There are a page layouts generated by applications, which include an EPS(JPEG) formatted image. However, when an EPS(JPEG) formatted image is subjected to a separation output process, a problem occurs in that only a K plate outputs.
Specifically, when a color image is subjected to the separation output process, color plates of C, M, Y, and K are obtained. In the EPS format, however, not only bit map data but also vector data of a line, a character, and the like can be included. For an application that performs the separation output process, extraction of the bit map data only from data in which the bit map data and the vector data mixedly exist is complicated and difficult.
Certain applications for creating a file in the EPS format can create a file so as to be subjected to the separation output process, which is usually difficult. Even in such applications capable of creating a file in the EPS format, it is still difficult to adapt to EPS (JPEG).
In the application performing the separation output process, in EPS (JPEG) image data, when a drawing code is not the K plate, an image is drawn in white, so that only the K plate is obtainable.
In some applications, by re-defining a process command on bit map data in a printer description language, the application is changed so as to print the other plates as well. The value of C, M, Y, or K per pixel is extracted corresponding to a plate and an image is formed on the plate. This enables a compressed image included in the EPS format to be separated into the colors of C, M, Y, and K.
However, when re-defining the process command in the printer description language, it is necessary to extract the value of color (value of C, M, Y, or K) pixel by pixel in accordance with a character sequence of the printer description language level. Consequently, this is problematic in that processing takes a long time.
When a Color Management System (CMS) provided for the image processing apparatus is used to deal with this problem, the process can be sped up. However, a CMS corresponding to conventional separation output has to use a one-dimensional Lookup Table (LUT) for a black and white image of each plate or, after rasterizing all of the plates, a multidimensional LUT for each of the pixels of C, M, Y, and K must be used.
For example, in order to realize color separation of a compressed image, it is necessary to convert a value of C to a value of K. It is difficult to perform such a process by using the one-dimensional LUT. After completion of rasterizing, color information is lost so it is difficult to perform the separating process.
There is also a method of rasterizing only the K plate in color without using the CMS, and also combining the outputted rasters of CMYK. According to this method, however, the overlap relation of objects (order in the vertical direction) is lost. It becomes difficult to accurately reproduce, particularly, overprinted objects.